Tape measures generally include a coiled tape that is spring biased towards a retracted position. A protective housing surrounds the tape and spring and includes an aperture through which a distal end of the tape extends. The distal end of the tape is pulled away from the housing during use in an extended position, and when released, the spring pulls the tape back into the housing such that the tape assumes the retracted position.
Various types of locking mechanisms are utilized for maintaining the tape in the extended position. Locking mechanisms are usually actuated by the user through a slide or push button positioned on an outer edge of the housing. Thus, the tape may be extracted to the desired length and the locking mechanism engaged to hold the tape at that distance. The locking mechanism may then be disengaged and the tape is retracted into the housing.
Many currently existing tape measures feature complicated locking mechanisms for holding the blade in the extended position. These locking mechanisms include a plurality of intermeshing parts which mate together and are selectively moveable between the open and engaged orientations. One drawback of these complicated locking mechanisms is that they result in a higher selling price to the consumer. The numerous individual pieces are often expensive to produce and assemble. Another drawback is that these complicated locking mechanisms are easily damaged if they are roughly handled, dropped, exposed to moisture or debris, and other like treatment.
Further, with existing locking mechanisms it is sometimes difficult for the user to determine when the mechanism is in an engaged or locked orientation. In one common embodiment, the device includes a thumb lock positioned on a front edge of the outer housing such as that disclosed in U.S. Pat. No. 4,489,494. The locking bar is selectively positionable between locked and unlocked orientations. As the thumb lock is slid from the unlocked towards the locked orientation, it is difficult for a user to determine whether it is in a full locked position that will restrict the tape from being retracted into the housing. Preferably, the locking mechanism provides for a definitive locked position in which the user can be assured that the locking mechanism is fully engaged to restrict retraction of the tape blade.
Thus, there is a need for a locking mechanism having a minimum of moveable parts, have adequate durability for use in harsh environments, and be positively locked in an engaged orientation to prevent tape retraction.